Multiple spindle, rotary indexing machine tool equipment, particularly of the type described in the Bullard et al. U.S. Pat. No. 2,947,188 has enjoyed a high degree of acceptance in the industry over a long period of years. The equipment is well suited to the repetitive, mass production of rotary machined parts, where the need is to produce extended high production runs of identical parts. In the automotive industry in particular, the equipment referred to above, commercially known as the Bullard "Mult-Au-Matic" Vertical Chucking Machine, has enjoyed a great deal of success.
Notwithstanding its many and important advantages, multiple spindle rotary indexing machine tool equipment of known design has had certain limitations in its capabilities, relating particularly to the degree of precision obtainable, and to the types of machining operations capable of being carried out. Accordingly, it is a primary objective of the present invention to provide a practical modification to the "Mult-Au-Matic" type multiple spindle rotary indexing machine tool, which retains its significant advantages, yet which at the same time enables the finished part to be delivered machined to higher orders of accuracy than heretofore possible and in finished forms heretofore impossible or impracticable to achieve.
In multiple spindle indexing machines of the type described in the before mentioned Bullard et al. U.S. Pat. No. 2,947,188, the machine includes a fixed circular base provided with a vertically upstanding central column. A circular worktable is rotatably supported on the base and carries a plurality of rotary spindles. For example, the circular worktable may have six equally spaced work stations, each containing a pair of work-holding spindles. The circular worktable is incrementally indexable about the central column, so that the individual sections are progressively indexed into different machining positons. Desirably, in a machine having six work stations on the worktable, there are five machining positions spaced about the central column, and a sixth position used for unloading of the finished work and loading of new rough pieces onto the spindles.
At the top of the vertical column, there is mounted a single drive motor, which operates all of the basic functions of the conventional equipment, including rotation of the spindles, indexing of the worktable and feeding of cutting tools. Each of the machining stations of the column has associated with it, mounted on the platform above, a mechanical feed works, driven from the primary motor and arranged with various change gears for controlling spindle rotational speed and tool feed rates at that machining station.
After rough parts are mounted on the spindles at the loading station, the table indexes progressively around the column. At each machining station, a particular machining operation is performed, and the spindle speeds and tool feed rates at that station are appropriately set to the operations performed. After a given operation is completed, and the tools are retracted, the table automatically indexes one position, and different machining operations are performed at the next machining station. When the equipment is operating on a steady state basis, the finished parts are successively indexed into the load-unload position, where they are removed and replaced by new rough parts. The parts then progress step by step around the central column, being machined in a particular manner at each of the five machining stations.
Because of the basic nature of the equipment, in which each of several worktable positions are successively associated with each of several different machining stations, there are inherent limitations to the ultimate accuracy achievable. In general, as a practical matter, tolerance of about 0.0005 inch are about as low as can be consistently maintained. Likewise, the arrangement of the feed works is such that contour machining and/or threading operations, for example, are not practical.
In accordance with the present invention, a multiple spindle rotary indexing machine tool is provided which, while retaining the basic functions and advantages of the known and tested equipment, renders such equipment greatly more versatile by enabling threading and contouring operations to be carried out and, in addition, enabling machining operations to be carried out to significantly greater levels of accuracy, for example, to tolerances of 0.0001 inch. In general, this is accomplished by modifying the equipment at one or more (but less than all) of the machining positions, typically the one prior to the load-unload positions, such that all functions, both tool advance and spindle rotation, are performed independently of the primary machine drive and under the control of a computerized numerical control system. With this arrangement, not only as it possible to perform complex contouring and threading operations at the modified machining stage, but further, the minor dimensional variations in the equipment, from one index position to another, may be readily compensated for, in order to provide increased levels of machining accuracy.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompanying drawings.